The present invention relates to a heat exchanger assembly for heat exchange treatment of substances or mixtures of substances, for example in which the application of a heat differential produces a change in temperature of a substance or a partial or complete change of state of a substance. The invention is particularly suitable for use in heat exchangers, evaporators and freeze crystallisation systems, particularly, but not exclusively, in the food, pharmaceutical and chemical industries. In particular, the invention is suitable for use in heat exchanger systems for treatment of fluid foods such as, for example, in pasteurisation of fruit juices or dairy products such as milk or yoghurt.
Tubular heat exchangers are commonly used in the food industry for heating or cooling of fluid food products. By the very nature of the products that they carry, the heat exchangers need to be inspected and vigorously cleaned on a regular basis to prevent build-up of solid organic or inorganic matter. Fatty or proteinaceous deposits will accumulate where conditions allow fouling to occur or, depending upon the role of the heat exchanger, through searing or freezing to the inner walls or the tubes of the heat exchanger. Inevitably, therefore, a substantial amount of production time and hence production efficiency is lost through these routine maintenance measures.
In some installations, the problem of residue accumulation around the inner walls of the heat exchanger product-carrying tubing is exacerbated by measures taken to enhance turbulence within the heat exchanger tubes. These commonly involve provision of turbulence-inducing projections or fins on an inner surface of the product tubing and along its length. Such turbulence-inducing fins or other projections are desirable to enhance the effectiveness of heat exchange but their side effect in increasing the surfaces on which residues may accumulate is decidedly undesirable.
Various arrangements specifically for cleaning heat exchangers are known, which arrangements typically comprise a scraper of some form passing along the heat exchange tube. A number of problems arise with such arrangements for example, the scraping of the product tubes causes the scraper to be worn away, thereby losing contact with the inner walls of the product tubes and allowing deposition of solid matter on to the walls of the product tubes. As a result of this, such systems require frequent maintenance, resulting in the loss of a substantial amount of production time and hence production efficiency. In addition, it is often necessary to replace the entire scraper each time.
EP0453043A describes a heat exchanger system in which solid particles are introduced into the product tube to clean its walls. These solid particles enter one end of the product tube and traverse its length until they are discharged from its other end. The solid particles are then directed to a collector where they are cleaned and fed back into the heat exchanger. A disadvantage of this system is that it requires the isolation, cleaning and reintroduction of the solid particles after each pass through the product tube, which is time consuming and cumbersome.
FR2224728 discloses the use of a scraping device within a heat exchanger product tube. A central rod is spirally wound with the scraping means, which contacts the inside of the product tube. However this arrangement suffers from a number of the problems identified above.
It is a general objective of the present invention to provide an improved heat exchanger assembly which is adapted to mitigate or overcome these and other problems of the prior art.
According to one aspect of the present invention, there is provided a heat exchanger assembly which comprises an elongate casing housing at least one product conduit extending substantially longitudinally therethrough and with a void surrounding the product conduit receiving, in use, heat exchange service fluid flowing therethrough, characterised in that the assembly further comprises a rod extending through the product conduit, said rod being moveable in a reciprocating manner along the conduit and having a scraping means radially projecting therefrom such that upon reciprocation of the rod within the product conduit, the scraping means scrape product residues from the inner walls of the product conduit.
Preferably, the assembly has a plurality of conduit tubes extending substantially longitudinally through the casing and a plurality of rods, each rod extending through a conduit tube, the rods being moveable in a reciprocating manner together by a common reciprocating drive means.
The plurality of rods may be mounted in a base plate that is housed within the casing or an extension of the casing to move with the base plate, the base plate being moved in a reciprocating manner by the reciprocating drive means.
The scraping means suitably comprises a scraping head mounted upon an arm projecting radially from the rod, and the scraping head may be moveable along the arm and biased by resilient biasing means.
The scraping means may have an arcuate radial outer surface. The scrapers are preferably arranged at different radial orientations along the length of the rod, and may be arranged in groups of two or three scrapers at intervals along the length of the rod with each member of the group at a different respective radial orientation.
The assembly may be adapted to function as a pump through use of a valve in the product fluid inlet.
Preferably, the assembly further comprises a controller to control the reciprocation of the rod(s) at predetermined intervals or in response to sensed temperature of the product or service fluid.
Preferably, the product conduit is a tube, which may have a circular cross section.
According to another aspect of the present invention there is provided a heat exchanger assembly which comprises a casing housing at least one product conduit extending substantially therethrough and with a void surrounding the product conduit receiving, in use, heat exchange service fluid, characterised in that the assembly further comprises a mount extending through the product conduit, said mount being moveable in a reciprocating manner along the product conduit and having a turbulence generating member projecting therefrom, such that upon reciprocation of the mount within the product conduit in use, the member causes turbulence within the product conduit.
A plurality of turbulence generating members may be provided, preferably with each member positioned at a different orientation around the axis of the mount.
Preferably the turbulence-generating member has a triangular cross section, wherein each corner of the triangle substantially contacts an inner surface of the product conduit. The corners of the triangular member may be curved or rounded off slightly.